Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$16.36	10.226%	$18.033	$18.03	$18.05	$18.00
Purchase #2	$18.36	11.826%	$20.5313	$20.53	$20.55	$20.50
Purchase #3	$165.78	12.836%	$187.0595	$187.06	$187.05	$187.10
Purchase #4	$62.52	9.572%	$68.5044	$68.50	$68.50	$68.50
Purchase #5	$180.65	10.503%	$199.6237	$199.62	$199.60	$199.60
Purchase #6	$40.64	11.173%	$45.1807	$45.18	$45.20	$45.20
Purchase #7	$98.65	10.866%	$109.3693	$109.37	$109.35	$109.40
7 purchase totals =	$582.96		$648.3019	$648.29	$648.30	$648.30